Procedure to get a document signed for construction in house

We are 4 brothers living with our mother in her house ,my elder brother wants to temporarily construction two rooms with kitchen with asbestos sheets roof on first floor and he agreed to sign an agreement concerning it and about vacating it with prior 2 months notice when ever asked.Now my questions are following 1.which amount of stamp paper should i use example 20rs,50, or 100 rs ). 2.do i need witnesses sign also for this agreement or my mothers sign and our signs are enough ? and if yes can my brother in law and sister can sign? 3.do i need to get notary done ?if yes then do my brother need to sign agreement in notary office in front of notary officer? 4.will this agreement will be lifetime valid or not?if not what i need to do to make it valid for life time